Disc drive memory systems are utilized in traditional stationary computing environments and also mobile environments including portable notebook computers digital cameras, digital video cameras, video game consoles and personal music players. These memory systems store digital information that is recorded on concentric tracks on a magnetic disc medium. At least one disc is rotatably mounted on a spindle, and the information, which can be stored in the form of magnetic transitions within the discs, is accessed using read/write heads or transducers. A drive controller is typically used for controlling the disc drive system based on commands received from a host system. The drive controller controls the disc drive to store and retrieve information from the magnetic discs. The read/write heads are located on a pivoting arm that moves radially over the surface of the disc. The discs are rotated at high speeds during operation using an electric motor located inside a hub or below the discs. Magnets on the hub interact with a stator to cause rotation of the hub relative to the stator.
Many disc drives utilize a spindle motor having a fluid dynamic bearing (FDB) situated between a shaft and sleeve to support the hub and the disc for rotation. The bearings permit rotational movement between the shaft and the sleeve, while precisely maintaining alignment of the spindle to the shaft. In a hydrodynamic bearing, a lubricating fluid is provided between a fixed member bearing surface and a rotating member bearing surface of the disc drive. These mobile devices are frequently subjected to various magnitudes of mechanical shock as a result of handling. As such, performance and design needs have intensified including improved resistance to shock events including axial and angular shock resistance, vibration response, and improved robustness. The read/write heads must be accurately aligned with the storage tracks on the disc to ensure the proper reading and writing of information. The stiffness of the fluid dynamic bearing is critical so that the rotating load is accurately and stably supported on the spindle without wobble or tilt. Moreover, a demand exists for increased storage capacity and smaller disc drives, which has led to the design of higher recording areal density such that the read/write heads are placed increasingly closer to the disc surface. Precise alignment of the heads with the storage tracks is needed to allow discs to be designed with greater track densities, thereby allowing smaller discs and/or increasing the storage capacity of the discs.
As a result of these intensified performance and design needs, and a need to meet operating requirements (including motor stiffness and power), motors for disc drive memory devices (i.e., 2.5 inch notebook motors) are typically marketed at two levels of performance, namely standard performance and high performance. The standard performance products commonly operate at about 5400 rotations per minute (RPM) rotational speed, while the higher performance products require a higher data access rate, which is typically achieved using a motor that operates at a rotational speed of about 7200 RPM. The high performance 7200 RPM products typically have higher manufacturing costs than the standard performance 5400 RPM products, and the high performance products typically sell at a lower volume, which results in a higher production cost due to manufacturing costs being spread over a smaller number of drives produced. Further, motors for desktop disc drive memory devices are also marketed at various levels of performance, namely low (i.e., 5400 RPM), medium (i.e., 7200 RPM) and high performance (i.e., 10,000 RPM), similarly resulting in higher production costs.
A different aspect of current notebook disc drive technology is the use of a low power mode to extend battery life in laptop computers. The low power mode, also known as idle mode, involves parking the read/write head on a ramp that is off a disc surface, and spinning the motor down to a lower speed while the drive is not being accessed. This power-saving “idle speed” is significantly lower than the “rated speed” (5400 or 7200 RPM) of the motor, but it is sufficiently high to maintain bearing clearances in the fluid dynamic bearing of the motor. The motor bearing viscous losses and the resulting run current are reduced by the square of the speed difference, while the bearing stiffness is reduced proportionally to the speed. Motor bearing stiffness requirements during the idle mode operation are not critical since the heads are parked and no read or write operations are occurring.